Femoroacetabular impingement (or FAI) is a condition of the hip joint where the femoral head and acetabulum rub abnormally, thus creating damage to the hip joint. The damage can occur to the articular cartilage of the femoral head or acetabulum, or to the labral cartilage on and around the acetabular rim. Increasingly, FAI is being recognized as a cause of significant hip pain and disability and is implicated as a cause of secondary osteoarthritis.
FAI may take one of two forms: cam or pincer. The difference between the two forms is determined by the abnormality of the hip joint that is the cause of the damage. The cam form of FAI occurs when the femoral head and neck relationship is aspherical, or not perfectly round. This loss of roundness contributes to abnormal contact between the femoral head and the acetabulum. It may also cause damage to the acetabular labrum, the peripheral cartilage that surrounds a portion of the acetabular rim. The pincer form of FAI occurs when the acetabulum has too much coverage of the femoral head. This over-coverage typically exists along the front-top rim of the acetabulum and results in the acetabular labrum and/or marginal articular cartilage being “pinched” between the acetabular rim and the neck of the femur. The cam and pincer forms of FAI may exist together (thus creating a compound form of FAI).
Cam or pincer FAI is commonly associated with other maladies to the bone and/or cartilage. For example, in some cases a portion of the acetabulum may contain a lesion. Contact between the femoral head and the lesioned portion of the acetabulum might create pain and discomfort in the patient. Damage to the patient's cartilage is often common with FAI—either the cartilage of the femoral head, the acetabulum, or the acetabular labrum. Patients with extensive FAI may experience tears of the cartilage due to excessive contact between the acetabulum and the femoral head. Damage to the cartilage may extend into the acetabulum.
Known treatments of FAI include surgical intervention to debride affected cartilage, combined with the use of osteotomy to reshape irregular bone (on either the femoral head or the acetabulum). For example, to treat cam-type FAI, osteotomy may be used to reshape the femoral head to be more spherical. For pincer-type FAI, osteotomy may be used in or around the acetabulum to trim any excessive coverage of the femoral head. The known treatments include “open surgery,” arthroscopy, or a combination of the two. In open surgery, the hip is dislocated through an incision of approximately 6 to 10 inches. Open surgery presents a high risk of blood loss and heightened recovery time. Arthroscopy may involve anywhere between two to four incisions, each of approximately 1 cm in length. The leg is placed in traction (in some cases, up to 50 lbs) to separate the hip joint and to make room for surgical instruments. Improper use of traction may cause nerve damage that may or may not heal with time. Additionally, arthroscopy presents poor visualization for the surgeon and requires significant training to become proficient. Finally, not all forms of FAI can be treated using arthroscopy. In combined surgery (also known as limited or “mini open” surgery), arthroscopy is used to repair acetabular labrum and cartilage, and a larger incision is made so that the surgeon may use osteotomy to reshape irregular bone.
These known treatments of FAI are limited to removing the patient's tissue: either debridement of soft tissue or osteotomy on the bone. The treatments are relatively new, and thus, long-term effects of the treatments are unknown. There is a concern that removing or reshaping the bone is not an effective long-term solution because the bone might grow back, thus requiring additional surgeries. Additionally, in these known treatments the cartilage and/or acetabular labrum are completely removed in order to obtain access to (and trim or reshape) the bone. No steps are taken to replace the removed tissue. Thus, after the patient's initial recovery from the surgery, the patient might experience pain due to the loss of the cartilage and acetabular labrum. For example, the patient would lose the “shock absorption” provided by these materials, and might experience pain due to bone-on-bone contact between the femoral head and the acetabulum. Additional surgeries may be required to address any issues caused by the loss of cartilage and/or regrowth of the bone. Finally, osteotomy on the bone might not be effective if the bone is irregularly shaped in that it has a depression (rather than a protruding portion of bone) or if the bone has a lesion. For example, although protruding portions of bone might be trimmed and reshaped easily, depressions cannot be reshaped because in a depression, there is little to no material to remove. Thus, the use of osteotomy on the bone may present several problems.
More recent developments involve the use of implants to replace and replicate the function of anatomy of the acetabulum and in particular the labrum, acetabular rim, and/or acetabular bearing surface. WO 2010/099247, the entirety of which is herein incorporated by reference, describes a variety of implants that may be positioned and fixed on the acetabulum to replace damaged cartilage (e.g., the labrum) and bone. FIG. 1 illustrates an embodiment of such an implant positioned on an acetabular rim 1004 in the acetabulum 1002 of a pelvic bone 1000. The implant 10 includes a rim portion 16 (which includes ridge 15) to replicate the acetabular rim and labrum and thereby capture the head of the femur within the acetabulum. The implant 10 also includes a bearing surface 18 that can generally align with the bearing surface 1006 of the acetabulum to provide a continuous surface on which the femoral head can articulate. The implant 10 wraps around at least a portion of the acetabular rim 1004.
In other embodiments, such as shown in FIGS. 2A-F, tools may be used to create prepared bone surfaces 1010, 1011 in a portion of the acetabulum 1002 and/or acetabular rim 1004. The prepared bone surfaces 1010, 1011 may have roughly the same shape as the implant 10, such that the implant 10 fits onto the prepared bone surfaces 1010, 1011. The implants 10 can have varying geometries and can be provided with mounting holes 20 to secure the implant 10 to the acetabulum 1002 and/or acetabular rim 1004 with fasteners.